Priobe,
Measure the thread depth, type and bolt size. Call ARP and order the closest lengths.
If you are running aluminum heads, do the same for the header bolts. The bolts they call "header bolts" are usually 3/4" length. When you add the header flange, gasket and any locking device thickness, that length is a joke. I have found 1" length bolts work in my friend's 392 right off the shelf. I plan on ordering the same lengh for my FE. They will be trimmed if needed.
Steve
Nice engine detail. I really like the redundancy of the two fan belts